perf: round 5 — CalDAV cursor streaming, SPA interning gaps, NC href prefix, per-request micro-allocs

Seven benchmark-gated changes (benches/ROUND5.md; BEFORE/AFTER bench +
equivalence gate each, rollback rule as ROUND2-4 — two intermediate
CalDAV shapes measured worse and were themselves rolled back before
shipping):

- CalDAV whole-calendar responses (REPORT no-range/sync-collection,
  depth-1 collection PROPFIND, .ics GET): buffered double-residency →
  ONE window-ordered scan (MIN(start_time) OVER (PARTITION BY ical_uid))
  streamed through a PG cursor, pages cut at UID boundaries. TTFB
  23.3→11.0 ms (2.1x), peak heap 14.2→8.0 MiB at 4k events / 45→24 MiB
  at 12k, wall +9-15% (documented trade, ZIP-streaming class); both
  multistatus and ICS byte-identical to the buffered output. Rejected
  shapes kept in the doc: per-page GROUP-BY keyset (3-4x wall) and
  per-uid ANY hydration (~20 µs/index descent).
- SPA listing interning gaps: folder/recent/favorites resources handlers
  (and the WebDAV pseudo-root) called raw Arc::from per row for the
  closed display set ROUND3 interned — now intern_display/intern_mime,
  4→0 allocs/row, byte-identical Arc contents.
- NC PROPFIND child hrefs: username + parent path encoded once per
  request instead of per child (543→165 ns/row, 13→4 allocs); native
  WebDAV href drops its intermediate encode String.
- suggest enrichment: entity clone + field re-clones per keystroke row →
  consume + move (166.5→126.8 µs/200 rows, 20→7 allocs/row).
- list_readable_by returns the cache's Arc (246→128 ns warm hit, 4→0
  allocs) — deep Vec clone per DAV-selector request removed.
- CardDAV REPORT: borrowed props, reused href buffer, exact-size etag
  quoting (3.04→2.34 ms per 5k-contact getetag poll).
- Auth span records: user_id.to_string() per request ×3 →
  tracing::field::display.

Checks: cargo fmt, clippy --all-features --all-targets -D warnings,
cargo test --workspace (523 passed). Follow-ups (CardDAV streaming,
&[&str] id batches, ::text UUID casts A/B, share-landing join) recorded
in benches/ROUND5.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017aJu9ghvuT8WqC31ZEGTBA

src/application/adapters/carddav_adapter.rs

@@ -663,17 +663,27 @@ impl CardDavAdapter {
             ]),
         ))?;
 
+        // Borrowed straight out of the request — the old `clone()` copied
+        // the whole Vec of owned QualifiedName strings per REPORT (same
+        // fix the CalDAV surface got in ROUND4).
         let props = match report {
-            CardDavReportType::AddressbookQuery { props } => props.clone(),
-            CardDavReportType::AddressbookMultiget { props, .. } => props.clone(),
-            CardDavReportType::SyncCollection { props, .. } => props.clone(),
+            CardDavReportType::AddressbookQuery { props } => props,
+            CardDavReportType::AddressbookMultiget { props, .. } => props,
+            CardDavReportType::SyncCollection { props, .. } => props,
         };
 
+        // One reused href buffer for the whole listing instead of a
+        // fresh String per contact.
+        let mut href = String::with_capacity(base_href.len() + 48);
         for contact in contacts {
-            let href = format!("{}{}.vcf", base_href, contact.uid);
+            href.clear();
+            let _ = std::fmt::Write::write_fmt(
+                &mut href,
+                format_args!("{}{}.vcf", base_href, contact.uid),
+            );
             // `write_contact_response` generates the vCard on demand when (and
             // only when) address-data is actually requested.
-            Self::write_contact_response(&mut xml_writer, contact, &props, &href)?;
+            Self::write_contact_response(&mut xml_writer, contact, props, &href)?;
         }
 
         xml_writer.write_event(Event::End(BytesEnd::new("D:multistatus")))?;
@@ -701,10 +711,11 @@ impl CardDavAdapter {
             xml_writer.write_event(Event::Empty(BytesStart::new("D:resourcetype")))?;
 
             xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
-            xml_writer.write_event(Event::Text(BytesText::new(&format!(
-                "\"{}\"",
-                contact.etag
-            ))))?;
+            let mut quoted = String::with_capacity(contact.etag.len() + 2);
+            quoted.push('"');
+            quoted.push_str(&contact.etag);
+            quoted.push('"');
+            xml_writer.write_event(Event::Text(BytesText::new(&quoted)))?;
             xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
 
             xml_writer.write_event(Event::Start(BytesStart::new("D:getcontenttype")))?;
@@ -724,10 +735,11 @@ impl CardDavAdapter {
                     }
                     ("DAV:", "getetag") => {
                         xml_writer.write_event(Event::Start(BytesStart::new("D:getetag")))?;
-                        xml_writer.write_event(Event::Text(BytesText::new(&format!(
-                            "\"{}\"",
-                            contact.etag
-                        ))))?;
+                        let mut quoted = String::with_capacity(contact.etag.len() + 2);
+                        quoted.push('"');
+                        quoted.push_str(&contact.etag);
+                        quoted.push('"');
+                        xml_writer.write_event(Event::Text(BytesText::new(&quoted)))?;
                         xml_writer.write_event(Event::End(BytesEnd::new("D:getetag")))?;
                     }
                     ("DAV:", "getcontenttype") => {